In recent years, there has been used EUV lithography with miniaturization of semiconductors. EUV light is as short in wavelength as 13.5 nm and thus is immediately attenuated in the atmosphere. Therefore, wafer exposure apparatuses (EUV scanners) using EUV light need to have an exposure optical system set up in vacuum. In this case, a reticle stage is placed in vacuum, and thus the chuck mechanism of an EUV mask cannot use a vacuum chuck system but employs an electrostatic chuck system. The electrostatic chuck system requires a chuck region of a larger area as compared to the vacuum chuck system, to obtain a specific retaining force. Accordingly, it is necessary to use the most part of the back surface of the EUV mask as a chuck region.
In EUV lithography, as described above, since the most part of the back surface of the EUV mask is used as a chuck region, foreign matters make it prone to reside on the front surface of the chuck mechanism. If foreign matters get caught between the chuck mechanism and the EUV mask, the EUV mask is deformed to generate distortion on the patterned surface. This causes a problem that the pattern transferred onto a wafer is distorted. In addition, since the chuck mechanism is located within a vacuum chamber, it is necessary to return the inside of the vacuum chamber to the atmosphere pressure before cleaning the vacuum chamber to remove foreign matters. in this case, the EUV scanner is stopped for a longer time, which is a major factor in decreasing the operating ratio of the EUV scanner.